As the development of sophisticated information society progresses, there are growing needs for the protection of copy right of music and/or visual information etc. handled by digital equipment, or the protection of digital cash and private information handled by IC cards and the like.
For this reason, it is required for semiconductor devices which process or store such confidential information to take protective measures to improve tamper resistance in order to prevent a third party from analyzing the interior of the concerned semiconductor device by using fraudulent means.
Tamper resistance refers to a characteristic feature of software or hardware meaning the level of difficulty of the analysis (reverse engineering), unauthorized revision, or tampering of the internal structure such as a circuit etc., or stored data or programs etc.
Japanese Patent Laid-Open No. 2000-11129 discloses for example, a structure in which the thickness of an IC chip, which is flip-chip mounted onto a card-like substrate, is configured to be 0.1 μm to 20 μm. According to such structure, if it is attempted to take out the concerned IC chip from the card substrate, the semiconductor substrate will be destroyed and thereby disabled.
However, since it is difficult to handle an IC chip which is processed to be extra-thin, special manufacturing facilities are needed for the manufacture of such a semiconductor devices. Further, since the production yields or productivity will decline, there is a risk of significant increase in the production cost. Further, there is possibility that the IC chip is easily taken out from an IC card by means of chemical solution exposure or heating etc.
Japanese Patent Laid-Open No. 2004-62572 discloses a structure in which a leaf spring is stuck to the back surface of a semiconductor chip which is flip-chip mounted onto a substrate, with a reinforcing plate being stuck to the concerned leaf spring, and thereafter all the parts are sealed with sealing resin. According to such a structure, if it is attempted to take out a semiconductor chip from the module, the elastic force of the leaf spring will act on the semiconductor chip thereby destroying the concerned semiconductor chip.
However, in such a structure, it is difficult to reduce the thickness of the semiconductor device. Especially, when a leaf spring which has an enough elastic force to destroy the semiconductor chip is fixed to a reinforcing plate made of resin, the concerned reinforcing plate needs to have a sufficiently large thickness, thereby making it difficult to reduce the thickness of the semiconductor device. Further, when a chemical solution is used to dissolve and remove the sealing resin and the reinforcing plate, a portion which supports one end of the leaf spring will be removed and, therefore, the spring force of the leaf spring cannot be sufficiently transferred to the semiconductor chip even if the leaf spring recovers its elasticity, making it difficult to destroy the concerned semiconductor chip.
Japanese Patent Laid-Open No. H11-31208 discloses, for example, a structure in which a concave part is formed on the back surface of a semiconductor substrate. According to such structure, when stress is applied in an attempt to fraudulently detach the semiconductor substrate, the concerned semiconductor substrate will be readily destroyed. Further, according to such a structure, it is also possible to prevent the observation by an optical methodology using laser measurement etc.
However, in such structure, since a concave part is formed in the back surface of the semiconductor substrate, the reliability of the semiconductor device will be degraded.
Japanese Patent Laid-Open No. H11-204566 discloses a structure in which an integrated circuit chip, on the back surface of which a protection film for blocking observation, or bumps and dips for producing irregular reflection are formed, is mounted in a curved state on a wiring board. According to such structure, if the protection film for blocking observation or the bumps and dips for producing irregular reflection are machined to be removed by a mechanical method such as grinding or polishing, a part of the curved integrated chip will also be removed. Further, according to such structure, even if it is attempted to observe the circuit pattern on the surface of the substrate from the back surface of the semiconductor chip by using infrared ray etc., the observation will be hindered by the unremoved protection film or bumps and dips for producing irregular reflection.
However, in such structure, since an integrated circuit chip is mounted in a curved state on a wiring board, it is difficult to reduce the thickness of the semiconductor device. Further, since internal residual stress becomes larger, the reliability of the semiconductor device will decline. Furthermore, since special manufacturing facilities are needed when manufacturing the concerned semiconductor device, the manufacturing cost will increase.